Heating apparatus



1934 E. F. NORTHRUP HEATING APPARATUS Filed April 30, 1932' 3 Sheets-Sheet l Nov. 20, 1934. E. F. NORTHRUP HEATING APPARATUS Filed April 50, 1932 5 Sheets-Sheet 2 Patented Nov. 20, 1934 PATENT. OFFICE 1,981,632 name APPARATUS Edtzin Fitch Northrup, Princeton, N. 1., assignor Ajax Electrothermic Corporation,

Ajax

Park, Ewing'Township, N. 1., a corporation of New Jersey Application April .30, 1932, Serial No. 608,377 11 Claims. (01. 219%?!) My invention relates to secondary resistors or mume heaters, intended particularly for the purpose of heating travelling material, which may be fluid or solid.

The main purpose of my invention is to utilize secondary return loops extending away from the primary as a means of heating fluid or solid material progressed through the space near to the loops.

A further. purpose is to provide a chamber havingreturn loops extending into it like flns from either the outside or the inside according to the character of the chamber and to use this chamber as a muflie for heating fluid or solid 15 material.

' A further purpose is to use return loops extending inwardly or outwardly from a boundary wall in proximity'to an outer or interior primary inductor coil carrying an alternating current for the purpose of leading the inducedgcurrent to a distance from the inductor-and there applying.

the heat from it through selective. and predetermined heating of the return loops.

I Aturther purpose is to form reentrant electrically conducting return loops (webs, flns or ribs) whose interior position causes them to become excessively heated; and to apply these heated return loops to the heating of a fluid or to the predetermined selective heating of a solid body placed or passed in proximity to them.

A further purpose is to provide a mulile of alternatively solid or sectional construction, having an interior heating chamber for a charge, the heating chamber comprising inwardly projecting return loops (flns) in electrical circuits with an inductor secondary made up of conductors joining the ends of the return loops.

A iurtherpurpose is to provide bends of travel for fluids between side walls and outer or inner limiting walls which are parts of current paths transverse to the direction of fluid travel and which are inductively coupled with surrounding or interior primaries.

A further purpose is to form a clover-leaf construction in which the parts corresponding to the outer or inner clover-leaf limits are coupled with an operating current inductor primary and in which the parts between the latter limits are resions, as compared with the remainder of the secondary path, as by alteraticnot the cross sectional area or by the use of diflerent conductor materials for the two parts of the secondary.

A further purpose is to exaggerate the heating eflect of a secondary within inwardly or outwardly projecting return loops as compared with the heating effect in the portion of the secondary closely coupled to a primary by using relatively smaller conductor cross sections in the return loops or by constructing the return loops of ma- 'terial of relatively high resistivity.

A further purpose is to provide a muiile having a tapered opening for the purpose of determining the extent of heating of a solid charge passed 7 through the mui'fle. i

A further purpose is to pass a solid strip through a mume, instantaneously at variant distances from an interior muiile heating surface, for the purpose of heating portions of the strip to diflerent degrees.

A further purpose is to progressively enlarge or contract the available passage space or concentrate to differing degree the heating surfaces met with by a solid or fluid which is passing through'a furnace with the purpose and intent oi. altering the heating effect upon the charge at different parts ofits progress through the furnace.

A further purpose is to break up the length of a heating chamber through which fluid is to be passed and heated, and whose walls comprise arcuate secondary segmental portions and connecting return loops, and to stagger the return loops so as to act as battles to the fluid passing through and by the alteration of fluid flow to increase the heat transfer contact of the fluid against the return bends.

. Further purposes appear in the and in the claims.

My invention relates not only to the methods or processes involved but also to mechanism by which the methods or processes may be carried out.

I have preferred to illustrate my invention by a few iorms only among the many by which the invention may be carried out, selecting forms which are practical, effective and mechanically advantageous, but which have been chosen primarily because of their desirability in illustration of the invention.

Figure 1 is asection taken upon the line 11 of Figure 2, embodying one form of my invention.

Figure 2 is a section of Figure 1 taken upon the line 2-2 and adding circuit connections.

Figures 3, 4, 5 and 7 are sections correspond- 110 specification ing generally with Figure 2, but showing modifications. V 4 Figure 5 is a section upon the line 5-5 of Figure 6.

Figure 6 is a section taken upon the line 6-6 or Figure 5.

Figure 7 is a section taken upon the line 7-7 of Figure 8.

Figure 8 is a section upon the line 8-8 of resistor similar to that shownin Figures 9 and 10,

somewhat modified.

In the drawings similar numerals indicate like parts. V

I provide a very desirable form .of inductively heated muilie, in which the secondary normally follows the course of the primary, making diversions from the primary to lengthen the secondary path and to carry the heat to points where it may be more advantageously applied than immediately adjacent to the primary. These diversions are in the form of return loops, whose opposite sides are ordinarily parallel and so close together as to be non-inductive.

My invention is especially suitable for heating fluids, either liquids or gases, since the return loops form fins which assist in transferring heat from the secondary to the charge. My invention may also be used to considerable advantage to heat solid charges. The return loops may be positioned to form partition walls of a heating muffle, adjacent to or in contact with the charge.

Figures 1 and 2 show a heater for fluids having a muflle in the form of a cylinder. By the use of the word cylinder it is not intended to indicate that the muflle cannot be conical or the frustum of a cone, for example, nor that it must cal form isnot important and that other contours may be used if desired. The cylindrical form is selected for illustration because it is most con venient to manufacture and because it cooperates with a primary inductor coil of minimum cost.

In this form the primary may be any suitable inductor coil, preferably a hollow copper coil providing a minimum of resistance and an interior passage for water cooling.

The, secondary inductor 21 is a mufiie which, except for the fact that it is round instead of rectangular, is of the same general character as the inductor secondaries shown in my applications, Serial Nos. 484,120 and 484,121, filed September 24, 1930. In form all of my secondaries bear a relation to the secondaries of these two applications.

My secondary 21 is composed of a boundary wall 22, compri g segmental sections, and of return loops 23, which resemble fins, webs or ribs and extend inwardly, generally toward the axis Jf the secondary, which preferably is coincident with the axis of the primary. The fins, webs or ribs are slotted or otherwise separated at 24 so as to require the current induced within, the boundary wall 22 to travel, for example, at any instant, inwardly along the walls of the return loops 23 and outwardly along the walls 26, so that the two sides of each return loop are included in series with one another in circuit with the boundary wall 22.

' At the next reversal of the alternating current in the primary, the direction of the current in the return loops 23 and in the secondary generally will reverse, so that current will flow inwardly along the wall 26 and outwardly along the wall 25 of each return loop 23. i

At any instant, the currents in the opposite walls 25 and 26 of the return loops 23 are always equal and opposite, and the walls are relatively close together, being separated only by the slots 24, so that the return loops are non-inductive. This makes it possibleto maintain a low secondary inductance, notwithstanding that the return loops 23 may represent a considerable proportion of the total length of the secondary path.

Though current-carrying return loops thus formed, connected with the segmental sections of the secondary in close coupling with the primary, are aptly. designated as reentrant where they extend toward the common axis-in this case of the primary and of the segmental sections of the secondary, as shown in this formit has seemed necessary to coin a word to designate these return loops when they extend outwardly as in Figures 7 and 8; in which case I have called them exentran The thought is that return loops" will serve as abroad term to cover both, under which term reentrant and exentrant are oppositely extending species. r

The cylinder-whatever its exact contour and shape-terminates in end walls 27 and 28, forming a closed compartment 29, with which connection is made at 30 and 31, either of which may be the inlet and the other the outlet. Obviously there will be advantage for certain specific uses in having one or the other of these directions of fluid flow, either to havethe greatest contact between the walls of the container and the fluid at the top or at the bottom.

In the absence of specific benefit otherwise, the direction of flow will be assumed to be from the bottom to the top as in the arrow of Figure 2, since the flow of fluid-through the heater is then assisted by the natural rise of hotter fluid toward the top.

The-space between the primary and the secondary is filled with any suitable heat insulation 32 which may or may not insulate electrically at the same time. In the illustration an electrically insulating sheet 33 is shown immediately adjoining .the primary, which serves the purposes, not only of electrically insulating the primary, but of acting as a container or limitation for the insulating material appearing at 32.

The circuit connections for supplying current to the primary inductor may be of any suitable type. In Figure 2 I show an alternating current source 34 connected to the primary 20 by leads 35 and 36, with capacity at 3'7- to resonate the circuit.

The current induced within the various segmental sections of the secondary passes from segment to segment through the return loops 23, highly heats the walls of the return loops and consequently lfighly heats the fluid which comes into contact with them.

. The large surface of contact is effective in rapid heating of the fluid, whether it be liquid, gaseous, or solid in finely divided form, and the spacing of the walls of difierent return loops connected with opposite ends of the same segment, makes the mechanism effective even where some leakage 913 induced current takes place through a slight of the chamber 29, the end plates 27 and 28 are electrical conductivity of the fluid heated. It will be noted that the spaces of separation 24 between adjoining walls of the same return loop are not accessible to the fluid heated, with the result that there can be no short circuiting of electricity across from a wall 25 to a wall 26 of the same return loop.

In order to avoid short circuiting at the ends slotted or otherwise divided in line with the separations 24 between the walls 25 and 26 ofthe return loops, with the purpose and intent that the only connection between the adjoining parts of the return loops shall be through the segmental sections inductively coupled with the primary.

By showing the inlet and outlet as relatively small pipes at the axis, it is not intended to indicate that these need be confined to any such dimensions. In fact, the size of opening will be dependent in large measure upon the rapidity of heating, and the nature of the charge.

The range of materials which may be treated in a heater of the type of Figures 1 and 2 is very wide, and includes fluids generally, both gases and liquids, with or without the admixture of solid material. As examples merehr of the uses to which my heater may be applied, I suggest the heating of water or oil, the distillation of zinc, the heating of gases such as mixtures of sulphur dioxide and air preliminary to introduction into a sulphuric acid converter, and the heating of reacting components to carry on chemical reactions in the chamber 29, especially where accurate temperature control throughout the reaction is desirable.

In Figure 3 the structure is the same as that in Figures 1 and 2, except that in Figure 3 the secondary mume is made up of anumber of short units 21' which flt one upon the top of another, and, with end units 27' and 28', make up a complete mufiie' unit and that the heat and electrical insulation have not been indicated between the primary and the secondary. The coil 20 shown is shorter with respect to its diameter and the secondary is also shorter with respect to its diameter than in Figures 1 and 2, a matter largely of convenience and speed of treatment. With the shorter mufile, the fluid heated must be kept in the muille a longer time to reach the same temperature as with the longer muflie or must be more rapidly heated within the muille.

In Figure 4 the same primary 20' is shown as in Figure 3, but the secondary is formed in a single piece and has its return loops 23 tapered longitudinally of the muflle. The tapered edge 38 comes much closer to the axis than the tapered edge 39. The slope of the tapered edge 38 is different from that of the tapered edge 39, giving a different rate of heating and a different ultimate temperature of heating to the two sides of the charge 40.

In the example shown, the charge 40 is a band saw blade, desirably progressed through the muffle in the direction of the arrow preliminary to quenching. The thed edge 41 is heated somewhat more rapidlyand to a higher temperature than the back edge 42, in the form illustrated.

'Manifestly the return loops 23 may be arranged in'many variant shapes to suit the needs of a particular heat treatment, concentrating the heat exactly where it is desired.

This structure, as that of Figures 1 and 2, could of course be made in short units as inFigure 3, if desired. l

' In Figures 5 and 6 I show a form very similar to avoiding the intimate contact with the loops 23 which assist in heat transfer, the center of the mume between the ends of the return'bends is filled with refractory 43, desirably consisting of the heat absorbing material known in the art as radiant" material. Grooves at 44 and 45 in the ends of the refractory 43 permit communication between the inlets and outlets of the muflie and the annular space between the return loops.

In order to avoid short circuiting of one muille portion 21' by another, due to the nonfl try of the spaces 24 between the sides of the return loops, I interpose electrical insulation 46 between different mufile sections. Leakage from the muflle through the spaces 24 is prevented by fllling the spaces with a suitable refractory'cement at 24'.

The form of Figures 5 and 6 is chiefly advantageous because it serves to bring the charge into intimate heat transfer contact with the return loops 23, since the space between the return loops follows a spiral course throughout the length of the muiile, while at the same time the sides of the spiral are irregular and the fluid is constantly changed in direction around the return loops 23.

It is of course evident that many other arrangements may be designed to bring the charge into frequent and intimate contact with the return loops, which develop heat in the muffle interior.

I find it very advantageous to have the inductor coilfollow a boundary wall of the muflie, so that a relatively large surface is provided in which the secondary current may be produced, and the induction of the secondary current may occur at intervals with intermediate diversion of the secondary current into theinterior of the muffle for heating However, the boundary wall used need not necessarily be the outside boundary wall, but may be the inside boundarywall as shown in' Figures 7 and 8.

In these flgures, the inductor coil 20"lies within and in inductive relation with the inner mufile boundary wall, comprising the secondary resistor 21. The return loops 23, in this case are exentrant rather than reentrant, but are otherwise identical with those seen in Figures 1 to 6. As in Figures 3, 5 and 6, the muflie wall is made up of a series of units.

The muffle is provided with a refractory casing 47 and a refractory cover 48. The cover may be removed for insertion of a solid charge, while a liquid charge may be inserted and withdrawn through openings 30 and 31.

It will be evident that the form of Figures '7 and 8 using the exentrant return loops 23, may be used in structures embodying any of the other special features of my invention as herein outlined.

In muflies of the type described by me it is of considerable importance that the heating take 'place well within the muiile where the heat proshown. I do not include the return loops 23 and 23' in the designation of boundary walls, as they 5 are essentially fins extending into the muilie interior. I

In Figures 9 to 11 I show two forms of muiiie wall or secondary resistor in which the heating is concentrated in the return loops as distinguished from the boundary walls by relatively increasing the resistance of the return loops. As is well known, the power consumed in a series circuit is in direct proportion to the resistance encountered, and therefore, in Figures 9 to 11, where the resistance of the return loops is relatively higher than that of the boundary walls, the power consumed and hence the heat developed in the return loops will be relatively greater than the power consumed and heat developed in the boundary walls.

Several difierent means for concentrating the heating in the return loops, as distinguished from the boundary walls, are available. The cross sectional area of the current path may be made smaller in the return loops than in the boundary walls, thus increasing the resistance, as indicated in Figures 9 and 10, the return loops may be formed of material having a higher resistivity than that used for the boundary walls, as shown in Figure 11 or both expedients may be adopted.

In the form of Figures 9 and 10, the boundary wall comprises series of segmental portions 49 of relatively large cross section, while the return loops 23 consist of material of relatively small cross section, as indicated at 50.

In operation, the current induced in the boundary wall 49 will chiefly be used up in heat in the return loops 23, because of the muchgreater resistance of the return loops on account of their smaller cross section. v

In the form of Figure 11, the segmental portions 49 consist of a material having relatively low resistivity, such as iron, while the return loops 23 comprise material of relatively high re-- sistivity, such as nichrome.

The segmental portions are joined to the return loops by any suitable means, forexample,

by the welds 51.

- The operation of the form of Figure 11 is substantially the same as that of Figures 9 and 10,

since the greater resistances of the return loops cause the bulk of the heat to bedeveloped in them.

It will be evident that the return loops of my invention are desirable adjuncts to secondary resistorsin order to cause development of the heat near to the center of the muflie. Besides developing the heat at or near to the pointwhere it is needed, the return loops act as fins to distribute heat by convection, radiation and conduction. By reason of the fact that they extend out into the muille, the return loops are particularly desirable to heat a fluid. By a fluid I mean to designate any substance which behaves as a fluid, that is, which is capable of flow, and I include in this designation liquids, vapors, gases, materials which are in molten condition at some stage during the heating processes, liquids or gases having solids in them, as for example, sludges, and finely divided solids. a

It will be evident that further advantage in heating fluids exists because the return loops cause solid-to-fluid heat transfer, which is much more eflicient than heat transfer through an intervening medium such as air. The fluids come 1,osi,es2

directly in contact with the return loops and they are changed in direction by the return loops, thus causing the fluids to take'a circuitous path and to come into intimate contact with the return loops, undergoing thorough mixing to bring all portions of the fluids into contact with the loops. This mixing may be obtained in any of the forms, but is most advantageous in the forms of Figures 5 and 6 where the charge cannot pass through the furnace without repeated change in direction.

It will also be evident that my return loops preferably carry the current from and back to the boundary wall in adjacent generally-parallel (I speak of parallel in the geometrical sense) paths, thus rendering the return loops noninductive. By avoiding increase in the inductance due to the return loops, I thus have a further distinct advantage, since the secondary inductance isnot increased by the use of the return loops.

In view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain part or all of the benefits of my invention without copying the structure shown, and I, therefore, claim all such in so far as they fall within the reasonable spirit and scope of my invention.

'Having thus described my invention, what I claim as new and desire to secure by Letters Paton is:

' 1. In an electric induction fumace, an inductor coil, means for supplying alternating current to the inductor coil, an electrically conducting muflle having a boundary wall in inductive relation with the inductor coil and having a return loop with electrically separate sides extending away from the inductor coil to cause the current induced in the boundary wall to take a longer path and means for passing a charge through the muflie, whereby the charge-may be heated by the return loop.

2. In an electric induction furnace, an inductor coil, means for supplying alternating current to the inductor coil, an electrically conducting muffle having a boundary wall in inductive relation with the inductor coil and having a return loop with electrically separate sides extending away from the inductor coil to cause the current induced in the boundarywall to take a longer path, the opposite sides of the return loop being adjacent and generally parallel so that the return loop is noninductive, and means for passing a charge through the muflie, where it can be heate by the return loop.

3, In an electric induction furnace, an inductor coil, means for supplying alternating current to the inductor coil, an electrically conducting muffle having a boundary wall in inductive relation to the inductor coil and having a plurality of return loops with electrically separate sides extending into the mufiie interior from the boundary wall and leading the secondary current developed in the inductor coil, an electrically conducting muffle having a boundary wall in inductive relation to the inductor coil and having a plurality of noninductive return loops with electrically separate sides extending into the muiiie-i nterior from the boundary wall to lead the secondary current developed in the boundary wall into the muflie interior and means for passing a charge through the muflie interior, where it can absorb heat from the return loops.

5. In an electric induction furnace, an inductor coil, means for supplying alternating current to the inductor coil, an electrically conducting muilie having a boundary wall in inductive relation to the inductor coil and having a return loop with electrically separate sides extending into the muiiie interior from the boundary wall and leading the secondary current induced in the boundary wall into the muflie interior and means for passing a fluid charge through the muiile and in contact with the return loop.

6. In an electric induction furnace, an inductor coil, means for supplying alternating current to the inductor coil, an electrically conducting muflle having a boundary wall in inductive relation with the inductor coil and having a plurality oi noninductive return loops with electrically separate sides extending from the boundary wall into the mume interior, leading the secondary current induced in the boundary wall into the muflie interior and means for passing a fluid charge through the muiiie in contact with the return loops to receive heat from them.

7. In an electric induction furnace, an inductor coil, means for supplying alternating current to the inductor coil, an electrically conducting mume having a boundary wall in inductive relation with the inductor coil and having, extending from the boundary wall into the muiiie interior, a return loop with electrically separate sides, the resistance of the loop per unit length being greater than the resistance per unit length of the boundary wall, and means for introducing the charge into the muifle.

8. An electrically conducting muiiie having a boundary wall of relatively larger cross section and having a return loop with electrically separate sides, extending from the boundary wall into the muine, or relatively smaller cross section than the boundary wall, whereby the heat produced by an electric current through the boundary wall and through the return loop will be concentrated in the return'loop.

9; An electrically conducting mume having a boundary wall formed of material-oi relatively lower resistivity and having a return loop with electrically separate sides extending from the boundary wall into the muiiie interior formed of material of relatively higher resistivity than the boundary wall material.

10. In an electric induction iurnace, an inductor coil, means for supplying alternating current to the inductor coil, an electrically conducting muflle within the inductor coil and in inductive relation to it having a boundary wall and a return loop with electrically separate sides extending into the muiiie from the boundary wall andmeansiorpassingachargethroughthe muilie.

11. In an electric induction furnace, an inductor coil, means for supplying alternating current to the inductor coil, an electrically conducting muiiie within the inductor coil in inductiverelationtoit,l'iavingaboundarywallami having a noninductive return loop with electrically separate sides extending from the boundary wall into the muille and means for passing a charge through the muflie.

12. In an electric induction furnace, an inductor coil, means for supplying alternating current to the inductor coil, and an annular electrically conducting muiiie within the inductor coil having a. boundary wall comprising a plurality of segments and having a plurality of return loops with electrically extending sides electrically connecting the segments and extending into the muiile from the boundary wall.

13. In an electric induction furnace, an inductor coil, means for supplying alternating current to the inductor coil, an annular electrically conducting muflie within the inductor coil and in inductive relation to it, having a boundary wall consisting of segments and having a plurality of return loops with electrically extending sides electrically connecting the segments and extending into the muflie from the boundary wall, the sides of the return loops being adjacent and generally parallel so as to render the loops noninductive.

14. In an electric induction furnace, an inductor coil, means for supplying alternating current to the inductor coil, an electrically conducting muiile within the inductor coil and in inductive relation to it comprising a plurality of muflle units superimposed one upon another, each having a boundary wall and a return loop with electrically extending sides extending from the boundary wall into the muiiie, and means for passing a fluid through the muiile in contact with the return loops of the various units.

15. In an electric induction furnace, an inductor coil, means for supplying alternating current to the inductor coil and an electrically conducting .muflie within the inductor coil and in inductive relation to it, comprising units superimposed one upon another, each having a boundary wall and a plurality .of return loops with electrically extending sides extending from the boundary wall into the muiiie, the return loops of the respective units being staggered lengthwise oi the muiiie. I

16. In an electric induction iumace, an inductor coil, means for supplying alternating current to the inductor coil and an electrically conducting muifle surrounding the inductor coil, having a boundary wall in inductive relation with the inductor coil and having a return loop with electrically extending sides extending away from the inductor coil.

17. In an electric induction rurnace, an inductor coil, means for supplying alternating current to the inductor coil, an electrically conducting muiiie having a boundary wall in inductive relation with the inductor coil and having a return loop with electrically extending nnwm r rrcn noa'raaor. 

